Night vision systems include image intensification, thermal imaging, and fusion monoculars, binoculars, and goggles, whether hand-held, weapon mounted, or helmet mounted. Night vision systems are typically equipped with one or more image intensifier tubes to allow an operator to see visible wavelengths of radiation (approximately 400 nm to approximately 900 nm).
In conventional panoramic night vision systems, two separate monocular subassemblies are provided. Each monocular subassembly includes two image channels. Each of the image channels may be provided by an objective assembly that transmits an image from a viewed object to an image intensifier tube that intensifies the luminance of the image, and outputs the intensified image to another optical assembly, such as an eyepiece.
The panoramic effect of such a night vision system is achieved by angling the optical axes of each of the two image channels of each monocular relative to one another, but having partially overlapping fields of view. The separate image channels must be combined, such as with the image combiner. If the optical axes of the separate image channels are not properly aligned, the image may be sheared.
Unfortunately, the location of the input and output optical axes of an image intensifier tube may vary from tube to tube. The variation in the location of the optical axes of image intensifier tubes must be accommodated during the manufacture or assembly of a panoramic night vision system in order to assure the proper alignment of the optical axis of each channel in a monocular. Conventionally, during manufacture of the night vision system the optical axis of the image intensifier tube is properly aligned with the optical axis of the assembly and the image intensifier tube is secured in place in the optical assembly to prevent shifting of the image intensifier tube. Securing the image intensifier tube in the optical assembly may include bonding the image intensifier tube to an adjacent component of the assembly, clamping the image intensifier tube in an axial manner using a retaining ring, etc.
While the above techniques may be able to overcome the problem of initial alignment of the image intensifier tube in the night vision system, optical tolerances are too high to allow replacement or removal of the image intensifier tube without realigning and re-securing image intensifier tube.
Alignment of an optical axis of an image intensifier tube with an optical axis of an optical assembly may also be desirable for single tube, monocular and binocular night vision systems or weapon-mounted scopes.
Fusion night vision systems have been developed that combine image intensification with thermal (infrared) imaging. Thermal sensors allow an operator to see people and objects because they emit thermal energy. The image intensification information and the infrared information are fused together to provide a combined image that provides benefits over just image intensification or just thermal imaging. Whereas typical night vision systems with image intensification can only see visible wavelengths of radiation, a fused night vision system provides additional information by providing heat information to the operator. The image intensification image and the thermal image may be optically or electronically fused together. Proper registration of the two images in an eyepiece improves system performance.